Soil-transmitted helminths Sina Helbig*, Akre M Adja**, Alia Tayea, Neil Arya December 2012 Prepared as part of an education project of the Global Health Education Consortium and collaborating partners *First author **Corresponding author
List of modules 1. Soil Transmitted Helminths 2. Hookworm and Toxocariasis and Guinea Worm 3. Filariasis and Onchocerciasis 4. Schistosomiasis and Cestodes Photo credit: http://www.pathobio.sdu.edu.cn/sdjsc/engparabook/ch087.htm Page 2
Introduction to Soil-Transmitted Helminths Nematode infections are the most common worldwide Most common in areas of poverty and with poor sanitation facilities/practice Part of the development takes place outside of the human body in soil Infection occurs in contact with parasite eggs or larvae in contaminated soil - direct or ingestion Photo credit: A. Tayea, 2007 Page 3
Introduction to Soil-Transmitted helminths Many of those infected are symptomatic (depends on the intensity of infection), although may be insidious and result in significant long term morbidity: Malnutrition, malabsorption, and anemia Impaired physical and cognitive development In more severe cases, overt disease: Intestinal obstruction, rectal prolapse, and abscesses Involvement of other organs/systems (e.g. ocular) Image source: http://www.nobledrugstore.com/blog/wp-content/uploads/2012/11/intestinal-parasites-treatment-with-anthelmintics1.jpg Page 4
Photo: http://www.who.int/wormcontrol/documents/fact_sheets/soil_transmitted_helminths/en/index.html Page 5
Three types of transmission TYPE 1: Direct Eggs are passed in stool, they hatch and re-infect within 2-3 hours by being carried from the anal margin to the mouth without reaching soil If they do reach soil, they do not require a period of development there Example: Enterobius vermicularis (threadworm) http://media.web.britannica. com/eb-media/35/9635-004-b6593992.jpg Page 6
Three types of transmission TYPE 2: Modified Direct Eggs are passed in stool into soil and undergo stages of development in soil Eventually ingested, hatch and release larvae which penetrate stomach wall and enter circulation Upon reaching the lungs, they are passed up the respiratory tract and re-swallowed reaches intestine, becomes adult worm Example: Ascaris lumbricoides (roundworm), Toxocara spp., Trichuris trichiura Ascaris Lumbricoides (roundworm) http://www.e-cleansing.com/wpcontent/uploads/2009/12/ascaris.jpg Page 7
Three types of transmission TYPE 3: Penetration of the skin Eggs are passed in stool into soil, hatch into larvae and undergo further development Penetrate the skin, reach circulation and lungs passed up the respiratory tract and re-swallowed Reaches intestine where it becomes an adult worm Example: Ancylostoma duodenale and Necator americanus (hookworms), Strongyloides stercoralis Necator Americanus (Hookworm) http://www.dpd.cdc.gov/dpdx//images/parasitei mages/g- L/Hookworm/Hookworm_filariform_C.jpg Page 8
List of module sections 1. Epidemiology 2. Risk Factors 3. Life cycle/biology 4. Symptoms 5. Diagnosis 6. Treatment 7. Control http://www.wsp.org/hygiene-sanitation-water-toolkit/graphics/cartoon-09.gif Page 9
Ascaris lumbricoides ROUNDWORM Intestinal Nematode Page 10
1.1 Epidemiology: Ascaris lumbricoides Most common helminth infection globally, infecting up to one third of the world s population Responsible for 10,000-20,000 deaths annually (CDC) Most common in tropical, sub-tropical areas, but also in rural areas in developed countries Mainly found where there are poor sanitation and hygiene practices Children particularly vulnerable because of behavior conducive to transmission of the organism More hand-to-mouth contact, hygiene habits More basic info on roundworm infections at http://www.cdc.gov/parasites/ascariasis/ Photo:http://u.jimdo.com/www45/o/s8d19dcd0a5c1 dda1/img/i7c8d2ba29174be18/1342921206/std/ima ge.jpg Page 11
1.2 Risk factors: Ascaris lumbricoides Faecal-oral transmission route Poor sanitation and/or personal hygiene Poor household and/or environmental hygiene Use of night soil (human excrement) as fertilizer for crops or gardens Geophagia (deliberate consumption of earth, soil, or clay) Most often seen in tribal and rural societies among children and pregnant women Photo:http://farm5.static.flickr.com/40 38/4173815367_a5044893a8_o.jpg Page 12
1.3 Biology: Ascaris lumbricoides Largest parasitic worm in humans Female: 20-25 cm x 3-6 mm (can grow up to 40 cm) Male: 15-31 cm x 2-4 mm Female can produce up to 200,000 eggs each day Inhabit small intestine Ingested eggs hatch in small intestine Larvae pass through intestine wall, migrate through the liver and heart up to lungs, and are coughed up and swallowed back into intestine Signs/symptoms can manifest along any stage of life cycle Photo: http://www.visualphotos.com/photo/1x602 7393/nematode_worms_ascaris_lumbrico ides_z180045.jpg Page 13
1.3 Biology: Ascaris lumbricoides 1) Immature ova is passed in stool into soil 2) Fertilization/development of embryo within 2-4 months 3) Fertilization/development of embryo within 2-4 months 4) Ingestion of ova with second stage 5) Rhabditiform larvae hatch 6) Penetrate mucous membranes of stomach, enter circulation traveling to lungs. Burrows through alveoli, passing up respiratory tract. 7) Swallowed a second time and enters esophagus reaching intestine where become adult worms Period from infection to first passage of ova in the stool is 60-70 days Page 14
1.4 Symptoms: Ascaris lumbricoides Larvae migration: Symptoms caused by actual physical presence and eosinophilic inflammatory response Loeffler s Syndrome: Damage to the lungs during migration (potentially fatal) May have fever, cough, sputum, asthma, skin rash, eosinophilia, radiologic pulmonary infiltration Charcot-Leyden crystals associated with lysed eosinophils When larvae reach circulation they can cause localized symptoms (may wander to brain, eye or retina causing granulomas) Photo:http://download.imaging. consult.com/ic/images/s19330 33207701568/mmc5-midi.jpg Page 15
1.4 Symptoms: Ascaris lumbricoides Adult worms: Light-moderate infections are often asymptomatic Heavy infection can cause intestinal colic Aggregate masses can cause volvulus, intestinal obstruction, or intussusception Wandering Ascarids Ileus from mechanical obstruction, bowel perforation in the iliocecal region, acute appendicitis, diverticulitis, gastric/duodenal trauma Blocking to the ampulla of Vater with pancreatic necrosis Photo: http://drugline.org/ail/pathography/277/ Page 16
1.4 Symptoms: Ascaris lumbricoides Adult worms: Wandering Ascarids continued Blocking of common bile duct with obstructive jaundice Entry of liver parenchyma with abscess Invasion of genital tract An Ascaris mass removed from a child in Kenya (see right) Page 17
1.4 Symptoms: Ascaris lumbricoides Nutritional: Ascaris can cause physiological abnormalities in the small intestine resulting in: Malabsorption of nutrients Nutritional deficiency Vitamin A deficiency (results in night blindness) Growth failure Cognitive impairment Photo:http://ars.els-cdn.com/content/image/1-s2.0- S1526054207001285-gr2.jpg Page 18
1.5 Immunity: Ascaris lumbricoides Humans acquire only partial immunity to re-infection Demonstrated in some children where Ascaris infection is hyperendemic Serology shows evidence of ongoing inflammatory processes (especially in individuals who developed immunity as compared with susceptible ones) Humoral immune reaction with Th2 response directed against the migrating larval stage Geographical variance in immune spectrum, suggesting some genetic contribution to immune system response to infection Page 19
1.6 Diagnosis: Ascaris lumbricoides Passage of worms in stool, at times through nose or mouth Eggs in faeces Fertile eggs measure 45 x 60 μm contains unsegmented embryo Non-fertile eggs measure 40 x 90 μm WHO definition of heavy infection is > 50,000 eggs/g of faeces High eosinophilia in larval ascaris, but not in adult infection (then suspect Toxocara or Strongyloides spp. infection) Radiography: cylindrical filling defects or string-like shadows better visualized by CT scans Photo:http://3.bp.blogspot.com/_lWVA0qu uxne/trq7cdxntxi/aaaaaaaaaby/udls rgqeysu/s1600/ascarisinmouthandnose.j pg Page 20
1.6 Diagnosis: Ascaris lumbricoides Serology: little role, due to cross-reactivity with other helminthic infections In many settings in developing countries, diagnosis of intestinal worms/parasites is largely clinical Suggested by cough, abdominal distension, or non-specific systemic symptoms such as failure to thrive For example, in field settings, small children presenting with cough and/or headache are often given the general diagnosis of IP (intestinal parasites) and given antihelminthic therapy Page 21
1.6 Diagnosis: Ascaris lumbricoides A fertilized Ascaris egg (see right) Page 22
1.7 Treatment: Ascaris lumbricoides Drugs of choice: Albendazole, Mebendazole, Pyrantel pamoate Levamisol, Ivermectin (less effective) Treatment of complications: Prednisolone therapy (hypereosinophilia) Supportive treatment with antispasmodics, nasogastric tube, IV fluids Rarely enterotomy is required Correction of nutritional status if evidence of impairment, supplementation Page 23
1.8 Control: Ascaris lumbricoides Efforts to disrupt the faecal-oral transmission cycle Improve sanitation facilities and their use Regular de-worming in risk areas and children Avoid using night soil (human excrement) or animal (particularly swine) faeces as fertilizer Where this is not possible, care to thoroughly wash, cook or peel fruits/vegetables produced Public education on importance of sanitation, hygiene and relationship with parasitic infections Photo:http://www.pseau.org/gif/couv_oms_soil_tra nsmitted_parasites_2003.jpg Page 24
Trichuris trichiura WHIPWORM Intestinal Nematode Page 25
2.1 Epidemiology: Trichuris trichiura Worldwide distribution more prevalent in warm, humid tropical regions Estimated 0.8 billion people are infected globally, greatest in Southeast Asia and to a less extent equatorial Africa and Central and South America (CDC) Mean intensity of infection is greatest in children aged 4-10 years, maximum prevalence usually attained before 5 years of age Further basic information can be found at: http://emedicine.medscape.com/article/788570-overview Photo:http://www.biolib.cz/IMG/GAL/17331.jpg Page 26
2.2 Risk factors: Trichuris trichiura Factors conducive to faecaloral transmission route Poor general hygiene and sanitation practices More common among children Using night soil to fertilize crops Poor food hygiene Photo:http://3.bp.blogspot.com/_rJRxVYdf8ZQ/R5jQs0kJC_I/AAAAAAAAAQg/ 1oCAuYBlR0k/s400/e-histol-life.gif Page 27
2.3 Biology: Trichuris trichiura Greyish-white worm, often slightly pink Lives in cecum and appendix Male: 30-45 mm long, thinner anterior portion (containing a cellular esophagus), thicker posterior portion, caudal curved extremity with a single spicule in the sheath which is studded with spines Female: 30-35 mm long, posterior half occupied by a stout uterus packed with eggs. Egg: 50x22 µm contains a single embryo Female worm produces 2,00-10,000 eggs/day for 5 yrs Photo:http://www.microbeworld.org/i mages/stories/twip/t_trichuris_adult_ male.jpg Page 28
2.3 Life cycle Worms live in cecum or appendix Eggs are laid unsegmented, embryonation takes 21d Can withstand cold temperatures but not desiccation Infection directly from contaminated feces Eggs hatch after being swallowed in the intestine, where the shell is digested by intestinal juices and the larva emerges in the small intestine Penetrates the villi and develops for a week until it re-emerges and passes to the cecum and colorectum attaches itself to the mucosa becomes adult Incubation period (period from ingestion of egg to appearance of egg in stool): 60-90d Page 29
2.4 Pathology: Trichuris trichiura Strongly related to worm burden/intensity Many cases asymptomatic or mild Non-specific symptoms such as abdominal discomfort, irritability in children Severe infections Spread throughout the colon to rectum hemorrhages, mucopurulent stools, dysentery, rectal prolapse Related mucosal damage may facilitate other infections, like Shigella, Entamoeba histolytica, Campylobacter jejuni Page 30
2.5 Symptoms Majority of infections are mild or asymptomatic o Epigastric pain o Nausea, vomiting o Distension, flatulence o Weight loss In asymptomatic cases, the worms live harmlessly in caecum/appendix Moderate infections o Growth deficit o Anemia Page 31
2.5 Symptoms Severe infections, Trichuris dysentery syndrome Severe chronic diarrhea or dysentery with blood and mucous in stool Dehydration, Rectal prolapse Colonic intussusception/obstruction Hypoproteinemia Chronic iron deficiency anemia Clubbing (condition affecting the fingers/toes in which the extremities are broadened and the nails are shiny and abnormally curved) Cognitive deficits often irreversible by anti-helminthic treatment Also associated with appendicitis in tropical areas Possibly due to super-infection with bacteria Clubbing definition - The American Heritage Medical Dictionary Copyright 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. Page 32
2.6 Diagnosis Often an incidental diagnosis during evaluation for other parasites (A. lumbricoides, E. histolytica) o Characteristic eggs in stool Kato Katz Method (WHO): characteristic barrel shape of eggs with two terminated polar plugs, brown outermost layer o Egg count enables quantification of intensity of infection o WHO defines severe infection > 10,000 eggs/g of feces Proctoscopy (if dysentery): numerous worms attached to the mucosa (reddened, ulcerated) Honeycomb appearance of the small intestine Page 33
Adult worms Eggs Photo credit of eggs: CDC. http://phil.cdc.gov/phil/details.asp Page 34
2.7 Treatment Albendazole or mebendazole o As single doses, several days may be required for severe infections o Note: regional differences in albendazole susceptibilities Combination albendazole with ivermectin Iron supplementation as necessary Page 35
2.8 Control As with other STHs, control involves breaking the faecal-oral transmission cycle o Improved sanitation o Improved hygiene, especially handwashing o Avoiding crops fertilized with human manure and thorough washing/disinfection of such foods before preparation Health education in communities, schools Regular de-worming o Also helps address other STHs Page 36
Strongyloides stercoralis Intestinal Nematode Page 37
3.1 Epidemiology: Strongyloides stercoralis Caused by parasitic roundworm Strongyloides stercoralis, or rarely S. fülleborni (parts of Africa and Asia, Papua New Guinea) Worldwide distribution, especially prevalent in tropical Central and South America, China, South-east Asia Estimated 200 million infected worldwide Unreliable estimates of global prevalence due to difficulties in diagnosis Infection ranges from subclinical to life-threatening hyper-infection and disseminated disease Photo:http://enfo.agt.bme.hu/drupal/ sites/default/files/strongyllarvama.jpg Page 38
3.2 Risk factors: Strongyloides stercoralis Risk factors for infection: Partly transmitted via percutaneous route Poor sanitation or hygiene Risk factors for hyper-infection: Immunocompromised state Pre-existing condition (e.g. underlying malignancy) Corticosteroid therapy or immune suppressive therapy Malnutrition, alcoholism, or HTLV-1 infection Page 39
3.3 Biology: Strongyloides stercoralis 2 forms: parasitic (internal) and free-living (external) 3 developmental forms: adult, rhabditiform and filariform (infective) larva Adult worm: 2.5 x 0.034 mm, tapers anteriorly and ends in a conical tail. Vulva in posterior third of body, prominent uterus containing 50 eggs (55 x 30 µm) Internal sexual cycle o Male worm disappears quickly from bowel after oviposition in intestine o Eggs hatch immediately in the bowel into male and female rhabditiform larvae, which pass out in the feaces to continue external sexual cycle Page 40
3.3 Biology: Strongyloides stercoralis External sexual cycle o Free-living rhabditiform larvae develop into living adults which copulate in the soil and produce eggs o Free-living female is smaller (1 x 0.05mm) than parasitic female. The vulva lies posteriorly and the uterus contains eggs (70 x 40 µm) o Parasitic and free-living rhabditiform larvae develop indistinguishably into filariform larvae, which can remain alive in the soil for many weeks Page 41
3.3 Life cycle Page 42
3.3 Life cycle - autoinfection In some circumstances the external cycle can be omitted o Filariform larvae develop internally and reinvade bowel or skin enter circulation migrate to lungs penetrate alveoli and travel up trachea swallowed and reach intestine o Usually a small population of adult worms maintains itself in the small intestine for many yrs (> 30) in the absence of further infection from the outside Page 43
3.4 Pathology Filariform larvae cause petechial hemorrhages at the site of skin invasion (usually perianal skin/buttocks or wrists) accompanied by intense pruritus and edema Upon migration through lungs, young worms may cause symptoms resembling bronchopneumonia with some lobular consolidation Female worms deposit eggs beneath the villi of intestinal mucosa Phtoto:http://www.drugswell.com/winow/+Rudolph' s%20pediatrics/13.6%20parasitic%20diseas ES_files/C13FF18.png Page 44
3.4 Pathology Severe infections o First stage larva develop in intestine bore into wall of duodenum and jejunum develop to adult stage produce ova while encysted in the bowel spread to lymphatic system enter circulation and reach liver, kidneys, gallbladder, brain, lungs and rarely myocardium Larva may carry microorganisms (e.g. E coli) which can cause overwhelming septicemia Incubation period: infection to appearance of rhabditiform (larvae in stool) ~1 month Page 45
3.4 Pathology S. stercoralis larva in intestinal biopsy Free-living adult female S. stercoralis, alongside rhabditoid larva Photo credit: both images from CDC-DPDx from http://www.dpd.cdc.gov/dpdx/html/imagelibrary/strongyloidiasis_il.htm Page 46
3.5 Immunity Achieved in many individuals after 3 primary infections Humoral antibody-mediated immunity o Initiated by infective stage larva with Type I reaction eosinophilic tissue response peripheral eosinophilia often with urticarial rashes o Produced antibodies often cross react with other helminths Cell-mediated immunity: elicited by adult and larval worms in the tissues cell mediated granulomatous reaction If cell-mediated immunity is suppressed (e.g. by drugs) generalized hyperinfection syndrome results, causing massive (often fatal) strongyloidiasis In persons co-infected with HTLV-1, production of IFNγ may decrease production of antibodies that take part in the immune response Page 47
3.6 Symptoms (uncomplicated disease) Cutaneous (uncomplicated disease) o Recurrent urticaria at sites of penetration of filariform larvae o Larva currens Pruritic, raised lesions Visibly migrating Pathognomonic for strongyloidiasis Abdominal (chronic, uncomplicated disease) o Epigastric pain (middle or LUQ) o Bleeding o Nausea, vomiting, diarrhea (may alternate with constipation) o Small bowel obstruction with severe infection o Weight loss *Can also have a dry cough or sore throat at the 6th 9th day of infection, although relatively rare in uncomplicated strongyloidiasis. Page 48
3.6 Symptoms (complicated disease) Severe complicated strongyloidiasis caused by massive tissue invasion in setting of debilitating disease, malnutrition, serious illness, immunocompromise (e.g. steroids or HTLV-1 coinfection) Hyperinfection with large larvae burden Enteritis, colitis, malabsorption Disseminated disease Fever Pulmonary: resembles closely tropical pulmonary eosinophilia, hypereosinophilia Pneumonitis Pleural effusion Abscess *In pulmonary involvement in disseminated disease, there can also be haemoptisis and shortness of breath. Page 49
3.6 Symptoms (complicated disease) Disseminated disease o Intestinal Severe abdominal pain, diarrhea Protein-losing enteropathy Generalized edema, abdominal distention Ileus, necrotizing jejunitis o Neurologic Headache Convulsions Stupor Meningitis (E. coli in 30% of immunocompromised patients) o Septicemia with enteric organisms Shock Multiple petechiae, periumbilical purpura Page 50
3.7 Diagnosis Raised IgE levels In later stages chronic moderate eosinophilia may persist for years o Leukocytosis up to 25K/mL o Eosinophilia 10-12K/mL Rhabditiform larva in stool, duodenal aspirate o Fecal examination methods or culture on charcoal at 26 C o Baermann technique: more sensitive than direct microscopy o Serial stool samples, as diagnostic yield for single sample is relatively low (30%) Kato-Katz method does NOT detect S. stercoralis o Explains why global prevalence might be underestimated Page 51
3.7 Diagnosis ELISA Serum IgG More sensitive than coprology (the study and analysis of feces, as for diagnostic purposes) but also labor intensive Prone to cross-reaction with other helminths and filariae Gelatin particle indirect agglutinin test is considered to be more practical than ELISA for mass screening Coprology definition - Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved. Page 52
3.8 Treatment Treatment recommended regardless if the infection is symptomatic given potential severity of hyperinfection Immunocompromised individuals (on steroids, chemotherapy, HIV, pre-transplantation etc.) should be screened and treated Drug of choice: ivermectin single dose repeated after 1 week, or daily for 3 days Less efficacious: albendazole, mebendazole, thiabendazole Decrease of efficacy in co-infection with HTLV-1 Page 53
3.9 Control Improve awareness of disease and risk factors o Especially in areas where infection related to occupational risks (e.g. rice fields) Improved sanitation and hygiene practices o Especially where disease is endemic Improve case detection and treatment to reduce reservoir, autoinfection Many control measures for Strongyloides also target other STHs! Page 54
Acknowledgments Thanks to Jenna Kelly, Shazeen Bandukwala and Melissa Whaling for critical editing. We appreciate Tim Brewer and Jackeline Alger for thoughtful review. Page 55
Credits Sina Helbig 1, Alia Tayea 2, Akre M Adja 3 Neil Arya 4 1: Boston University School of Medicine, Division of Infectious Diseases, Boston, MA, USA 2: Médecins Sans Frontières 3: Institut Pierre Richet, Université de Cocody Abidjan 4: Western University, University of Waterloo, McMaster University Contact narya@uwaterloo.ca
The Global Health Education Consortium and the Consortium of Universities for Global Health gratefully acknowledge the support provided for developing teaching modules from the: Margaret Kendrick Blodgett Foundation The Josiah Macy, Jr. Foundation Arnold P. Gold Foundation This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.